1. Field of the Invention
This invention generally relates to alignment of optical elements and in particular to alignment of a fiber optic with active or passive optical components.
2. Description of the Related Art
The telecommunications network serving the United States and the rest of the world is presently evolving from analog to digital transmission with ever increasing bandwidth requirements. Fiber optic cable has proved to be a valuable tool, replacing copper cable in nearly every application from large trunks to subscriber distribution plants. Fiber optic cable is capable of carrying much more information than copper with lower attenuation.
In a typical optical fiber, separate subscriber/data sessions are handled concurrently on a single optic fiber by means of modulation of each of those subscriber data streams on different portions of the light spectrum by what is known as xe2x80x9cwavelength division multiplexingxe2x80x9d (WDM). Current implementations of WDM involve as many as 128 semiconductor lasers each lasing at a specific center frequency within the range of 1525-1575 nm. Each subscriber DataStream is optically modulated onto the output beam of a corresponding semiconductor laser. The modulated information from each of the semiconductor lasers is combined onto a single optic fiber for transmission. As this digital signal is passed across an optical network, it will be subject at various intervals to amplification by, for example, Erbium doped amplifiers and dispersion compensation by, for example, optical circulators with coupled Bragg filters. At each node in the network, e.g. central office or remote terminal, optical transceivers mounted on fiber line cards are provided. On the transmit side, a framer permits SONET framing, pointer generation and scrambling for transmission of data from a bank of lasers and associated drivers, with each laser radiating at a different wavelength. On the receive side, the incoming signals are separated into channels detected by photo detectors, framed and decoded.
Throughout the network a broad range of active optical components such as lasers and photo detectors and passive optical components such as circulators and isolators and filters are utilized to process optical beams from individual optical fibers. Each junction between an optical fiber and these active and passive optical components requires extremely precise alignment between the fiber and component in order to maximize coupling efficiency. Alignment tolerances on the order of 0. 1 micron or less are common.
In order to achieve these tolerances a three step fabrication process is required for each completed assembly. In the first step an elaborate clamping fixture is used to clamp fiber and component relative to one another. Then either one or both of the fiber and component are manually brought into alignment using the micrometers and angle plates which make up the typical clamping fixture. In the second step the component and fiber are fixed to one another using epoxy or some other fastening method and the fixture is removed. The removal of the frame typically results in a release of strain or tension in the bond joining the fiber and component. This produces small but significant misalignment of the assembly, which in turn results in the necessity of a third and final assembly step. In the third step the completed assembly is reclamped in a temporary fixture and the fiber or component are struck with a hammer or other more precise instrument to bring them back into alignment. The above discussed process is very time consuming and labor intensive and accounts for a major portion of the finished assemblies cost.
What is needed are improved methods which reduce the time, cost and expenses associated with the alignment of fiber optic assemblies.
The current invention provides a method and apparatus for aligning optical components including lenses, filters, lasers, fiber optics, etc. It may be used with particular advantage for the alignment of a fiber optic with active or passive optical components. It is inexpensive to fabricate. It does away with the need for expensive setup equipment. It allows optical components to be aligned with a high degree of accuracy and permanence. It has a small form factor.
In an embodiment of the invention the apparatus for aligning at least a first optic element and a second optic element includes a frame and at least one sleeve. The frame defines a frame bore along a longitudinal axis thereof. The at least one sleeve defines an eccentric bore configured to contain a respective one of the first optic element and the second optic element. The at least one sleeve is rotatably coupled with respect to the frame bore to align the first optic element with the second optic element in a plane intersected by the longitudinal axis.
In an alternate embodiment of the invention the apparatus for aligning includes a frame and at least one pair of nested sleeves. The frame defines a frame bore along a longitudinal axis thereof. The at least one pair of nested sleeves each include a corresponding eccentric bore, with an inner nested one of said pair of nested sleeves coupled to at least one of the first optic element and the second optic element and an outer one of said pair of nested sleeves rotatably coupled to said frame bore to align the first optic element with the second optic element by an epicyclic motion of the at least one of the first optic element and the second optic element.
In still another embodiment of the invention a method for aligning at least a first optic element and a second optic element, at a selected location relative to one another is disclosed. The method comprises the act of effecting an epicyclic rotation of at least a selected one of the first optic element and the second optic element to align the optic elements at the selected location.